. 151 
has no colour answering exactly to the purple of 
GeofFroy. 
407. It is, however, our object rather to investi- 
gate the general causes which give rise to colour in 
vegetables, than to detail and describe their particu- 
lar varieties and hues. But if the colourable matter 
of vegetables were extracted in various ways, and 
submitted to the action of acid and alkaline agents, 
of known strength, and in various proportions, not 
only might a vast variety of tints be produced, but it 
would not be difficult to determine, by calculation, 
the relative proportions in which those agents, in dif- 
ferent instances, contributed to their formation. And 
were the fundamental colours properly defined, and 
their grades and varieties arranged, and classified ac- 
cording to the method of Werner, we might perhaps 
obtain not only a regular series or suite of colours, 
answering, in some degree, to the diversity found in 
nature, but might, also, arrive at comparative esti- 
mates of the proportions of acid and alkaline matter, 
by which they were respectively produced. 
408. Lastly, the colours of fruit experience 
changes similar, in many respects, to those of leaves 
and flowers; and, apparently, from the varied opera- 
tion of the same general causes. In their earliest 
state, many fruits are green ; but in the more advan- 
ced periods of growth, they assume different tints of 
colour. To the production of these colours, how- 
ever, the light of the sun seems to be necessary ; for, 
according to M. Senebier, neither peaches, pears, nor 
cherries, acquire their proper lively colours, if, at the 
period of ripening, they are secluded from the action 
